The present invention relates to rotary fluid pumps. More particularly, the invention relates to a rotary fluid pump which is free from adverse effects due to thermal expansion, easy to assemble, and which has a high volumetric coefficient.
When a conventional rotary fluid pump as shown in FIG. 1 is employed as a coolant compressor, its temperature during ordinary use will increase to a high value, typically 100.degree. to 150.degree. C., and therefore its internal components are unavoidably subjected to thermal expansion. Especially, it is desirable that the gaps 42 and 92 between the rotor 2 and the front housing 4 and between the rotor 2 and the rear housing 9 be as small as possible to improve the volumetric coefficient. However, if the gaps are made small, then the front and rear housings 4 and 9 are strongly pressed against the rotor 2 upon thermal expansion due to the normal temperature increase as a result of which the rotor may be thermally seized against the housings.
In order to protect the rotor 2 and the front and rear housings 4 and 9 from wear and seizure, heretofore the pump was so designed that the rotor 2 is axially movable and lubricating oil is applied to the gaps 42 and 92. In another construction, the pump was so designed that the sides of the rotor 2 are abutted against flexible plates, or the sides of the rotor 2 are covered with a self-lubricating material. However, these conventional pumps are disadvantageous in the following points. In the pumps using lubricating oil, the pump is intricate in construction and bulky in size. In the pump in which the sides of the rotor are covered with self-lubricating material, the rotor may be locally worn or the coating of self-lubricating material applied to the sides of the rotor may be worn away as a result of which the clearances provided by the gaps 42 and 92 are excessively increased.